US9308499B1 - Polyimide blend membranes for gas separations - Google Patents

Polyimide blend membranes for gas separations Download PDF

Info

Publication number
US9308499B1
US9308499B1 US14/496,789 US201414496789A US9308499B1 US 9308499 B1 US9308499 B1 US 9308499B1 US 201414496789 A US201414496789 A US 201414496789A US 9308499 B1 US9308499 B1 US 9308499B1
Authority
US
United States
Prior art keywords
polyimide
membrane
blend
polyimide blend
membranes
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Active
Application number
US14/496,789
Other versions
US20160089634A1 (en
Inventor
Chunqing Liu
Howie Q. Tran
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Honeywell UOP LLC
Original Assignee
UOP LLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by UOP LLC filed Critical UOP LLC
Priority to US14/496,789 priority Critical patent/US9308499B1/en
Assigned to UOP LLC reassignment UOP LLC ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: LIU, CHUNQING, TRAN, HOWIE Q
Publication of US20160089634A1 publication Critical patent/US20160089634A1/en
Application granted granted Critical
Publication of US9308499B1 publication Critical patent/US9308499B1/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D63/00—Apparatus in general for separation processes using semi-permeable membranes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0081—After-treatment of organic or inorganic membranes
    • B01D67/009—After-treatment of organic or inorganic membranes with wave-energy, particle-radiation or plasma
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/12—Composite membranes; Ultra-thin membranes
    • B01D69/125—In situ manufacturing by polymerisation, polycondensation, cross-linking or chemical reaction
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/58—Other polymers having nitrogen in the main chain, with or without oxygen or carbon only
    • B01D71/62—Polycondensates having nitrogen-containing heterocyclic rings in the main chain
    • B01D71/64—Polyimides; Polyamide-imides; Polyester-imides; Polyamide acids or similar polyimide precursors
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/58—Other polymers having nitrogen in the main chain, with or without oxygen or carbon only
    • B01D71/62—Polycondensates having nitrogen-containing heterocyclic rings in the main chain
    • B01D71/64—Polyimides; Polyamide-imides; Polyester-imides; Polyamide acids or similar polyimide precursors
    • B01D71/643—Polyether-imides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2323/00—Details relating to membrane preparation
    • B01D2323/30—Cross-linking
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2323/00—Details relating to membrane preparation
    • B01D2323/34—Use of radiation
    • B01D2323/345—UV-treatment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2325/00—Details relating to properties of membranes
    • B01D2325/02—Details relating to pores or porosity of the membranes
    • B01D2325/022—Asymmetric membranes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2325/00—Details relating to properties of membranes
    • B01D2325/34—Molecular weight or degree of polymerisation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2325/00—Details relating to properties of membranes
    • B01D2325/34—Molecular weight or degree of polymerisation
    • B01D2325/341—At least two polymers of same structure but different molecular weight

Definitions

  • This invention relates to polyimide blend membranes and methods for making and using these membranes.
  • Membrane-based technologies have advantages of both low capital cost and high-energy efficiency compared to conventional separation methods.
  • Membrane gas separation is of special interest to petroleum producers and refiners, chemical companies, and industrial gas suppliers.
  • Several applications of membrane gas separation have achieved commercial success, including N 2 enrichment from air, carbon dioxide removal from natural gas and from enhanced oil recovery, and also in hydrogen removal from nitrogen, methane, and argon in ammonia purge gas streams.
  • UOP's SeparexTM cellulose acetate spiral wound polymeric membrane is currently an international market leader for carbon dioxide removal from natural gas.
  • Polymers provide a range of properties including low cost, permeability, mechanical stability, and ease of processability that are important for gas separation.
  • Glassy polymers i.e., polymers at temperatures below their T g
  • Cellulose acetate (CA) glassy polymer membranes are used extensively in gas separation.
  • CA membranes are used for natural gas upgrading, including the removal of carbon dioxide.
  • the membranes most commonly used in commercial gas and liquid separation applications are asymmetric polymeric membranes and have a thin nonporous selective skin layer that performs the separation. Separation is based on a solution-diffusion mechanism. This mechanism involves molecular-scale interactions of the permeating gas with the membrane polymer. The mechanism assumes that in a membrane having two opposing surfaces, each component is sorbed by the membrane at one surface, transported by a gas concentration gradient, and desorbed at the opposing surface.
  • the membrane performance in separating a given pair of gases is determined by two parameters: the permeability coefficient (abbreviated hereinafter as permeability or P A ) and the selectivity ( ⁇ A/B ).
  • the P A is the product of the gas flux and the selective skin layer thickness of the membrane, divided by the pressure difference across the membrane.
  • Gases can have high permeability coefficients because of a high solubility coefficient, a high diffusion coefficient, or because both coefficients are high.
  • the diffusion coefficient decreases while the solubility coefficient increases with an increase in the molecular size of the gas.
  • both high permeability and selectivity are desirable because higher permeability decreases the size of the membrane area required to treat a given volume of gas, thereby decreasing capital cost of membrane units, and because higher selectivity results in a higher purity product gas.
  • gas separation polymer membranes such as CA, polyimide, and polysulfone membranes formed by phase inversion and solvent exchange methods have an asymmetric integrally skinned membrane structure.
  • Such membranes are characterized by a thin, dense, selectively semipermeable surface “skin” and a less dense void-containing (or porous), non-selective support region, with pore sizes ranging from large in the support region to very small proximate to the “skin”.
  • fabrication of defect-free high selectivity asymmetric integrally skinned polyimide membranes is difficult.
  • the presence of nanopores or defects in the skin layer reduces the membrane selectivity.
  • the high shrinkage of the polyimide membrane on cloth substrate during membrane casting and drying process results in unsuccessful fabrication of asymmetric integrally skinned polyimide flat sheet membranes using phase inversion technique.
  • US 2005/0268783 A1 disclosed chemically cross-linked polyimide hollow fiber membranes prepared from a monoesterified polymer followed by final cross-linking after hollow fiber formation.
  • U.S. Pat. No. 7,485,173 disclosed UV cross-linked mixed matrix membranes via UV radiation.
  • the cross-linked mixed matrix membranes comprise microporous materials dispersed in the continuous UV cross-linked polymer matrix.
  • TFC thin film composite membrane
  • the TFC membrane has a layer of a blend of polyethersulfone and aromatic polyimide with a thickness from about 0.1 to about 3 microns.
  • U.S. Pat. No. 8,337,598 disclosed a TFC hollow fiber membrane with a core player and a sheath UV-crosslinked polymer layer.
  • the selective thin layer on the non-selective porous layer of a thin film composite (TFC) membrane can be delaminated easily from the non-selective porous layer, which will result in significantly decreased selectivity for gas separations.
  • the integrally-skinned asymmetric membranes have a selective thin layer and a porous layer from the same membrane material and formed from the same membrane solution at about the same time. Therefore, the selective thin layer of an integrally-skinned asymmetric membrane cannot be delaminated easily from the non-selective porous layer.
  • the present invention discloses polyimide blend membranes and methods for making and using these membranes.
  • This invention pertains to polyimide blend membranes and methods for making and using these membranes.
  • This invention pertains to polyimide blend thin film composite or asymmetric membrane with either flat sheet or hollow fiber geometry.
  • polyimide blend membrane in the present invention refers to a membrane prepared from a blend of two or more polyimide polymers.
  • the present invention provides a polyimide blend membrane comprising a miscible blend of an aromatic polyimide I that comprises a plurality of repeating units of formula (I) and an aromatic polyimide II that comprises a plurality of repeating units of formula (II), wherein formula (I) is
  • n, m, o, and p are independent integers from 20 to 500; and wherein formula (II) is:
  • q and r are independent integers from 20 to 500; and wherein the weight ratio of said aromatic polyimide I to said aromatic polyimide II is in a range of 10:1 to 1:10.
  • the polyimide blend membrane in the present invention was prepared by blending an aromatic polyimide I with high permeability and an aromatic polyimide II with high selectivity for gas separation.
  • the polyimide blend membrane in the present invention showed improved permeability compared to the aromatic polyimide II and improved selectivity compared to the aromatic polyimide I.
  • the polyimide polymers used for making the polyimide blend membranes with high selectivities described in the current invention have a weight average molecular weight in the range of 50,000 to 1,000,000 Daltons, preferably between 70,000 to 500,000 Daltons.
  • the polyimide blend membranes in the present invention have undergone an additional UV cross-linking process.
  • the polyimide blend membranes in the present invention have UV cross-linkable benzophenone functional groups.
  • the cross-linked polyimide blend membranes comprise polymer chain segments where at least part of these polymer chain segments are cross-linked to each other through possible direct covalent bonds by exposure to UV radiation.
  • the cross-linking of the polyimide blend membranes provides membranes with superior selectivity and improved chemical and thermal stabilities compared to the corresponding uncross-linked polyimide blend membranes.
  • the polyimide blend membrane in the present invention can be either asymmetric integrally skinned membrane or thin film composite (TFC) membrane.
  • asymmetric integrally-skinned flat sheet or hollow fiber polyimide blend membranes in the present invention were prepared by a phase inversion process. In some cases, UV radiation was applied to the surface of the membrane to further improve the membrane selectivity.
  • the membrane dope formulation for the preparation of asymmetric integrally-skinned flat sheet or hollow fiber polyimide blend membrane with high selectivities for gas separations in the present invention comprises good solvents for the polyimide polymers that can completely dissolve the polymers.
  • Representative good solvents for use in this invention include N-methylpyrrolidone (NMP), N,N-dimethyl acetamide (DMAC), methylene chloride, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), dioxanes, 1,3-dioxolane, mixtures thereof, others known to those skilled in the art and mixtures thereof.
  • the membrane dope formulation for the preparation of asymmetric integrally-skinned flat sheet or hollow fiber polyimide blend membrane with high selectivities for gas separations in the present invention also comprises poor solvents for the polyimide polymers that cannot dissolve the polymers such as acetone, methanol, ethanol, tetrahydrofuran (THF), toluene, n-octane, n-decane, lactic acid, citric acid, isopropanol, and mixtures thereof. It is believed that the proper weight ratio of the solvents used in the present invention provides asymmetric integrally-skinned flat sheet or hollow fiber polyimide blend membrane with ⁇ 200 nm super thin nonporous selective skin layer which results in high permeances.
  • THF tetrahydrofuran
  • the thin film composite polyimide blend membrane described in the current invention comprises a thin nonporous selective separation layer comprising the polyimide blend described in the present invention and a porous nonselective mechanical support layer made from a material different from the polyimide blend described in the present invention or a polymer blend comprising a first polymer different from any of the polyimides in the polyimide blend described in the present invention and a second polymer that is the same as one of the polyimides in the polyimide blend described in the present invention.
  • the porous nonselective mechanical support layer described in the present invention with a low selectivity and high flux can be made from materials including cellulosic polymers, polysulfone, polyethersulfone, polyamide, polyimide, polyetherimide, cellulose nitrate, polyurethane, polycarbonate, polystyrene, polybenzoxazole, or mixtures thereof.
  • the weight ratio of PI-1 to PI-2 is 1:1.2.
  • the blend PI-1/PI-2-O-5Si2.5U asymmetric integrally-skinned hollow fiber membrane with 2.5 minutes of UV treatment showed high H 2 /CH 4 separation performance with H 2 permeance of 198 GPU and H 2 /CH 4 selectivity of 184 for H 2 /CH 4 separation.
  • the blend PI-1/PI-2-O-5Si2.5U asymmetric integrally-skinned hollow fiber membrane with 2.5 minutes of UV treatment also showed high CO 2 /CH 4 separation performance with CO 2 permeance of 74 GPU and CO 2 /CH 4 selectivity of 30.1 for CO 2 /CH 4 separation.
  • the invention provides a process for separating at least one gas from a mixture of gases using the polyimide blend membrane described herein, the process comprising: (a) providing a polyimide blend membrane described in the present invention which is permeable to said at least one gas; (b) contacting the mixture on one side of the polyimide blend membrane to cause said at least one gas to permeate the membrane; and (c) removing from the opposite side of the membrane a permeate gas composition comprising a portion of said at least one gas which permeated said membrane.
  • polyimide blend membranes described in the current invention are not only suitable for H 2 purification application, but also suitable for a variety of other gas separations such as CO 2 /CH 4 , O 2 /N 2 , and H 2 S/CH 4 separations.
  • membranes for separation of both gases and liquids are a growing technological area with potentially high economic reward due to the low energy requirements and the potential for scaling up of modular membrane designs.
  • Advances in membrane technology, with the continuing development of new membrane materials and new methods for the production of high performance membranes will make this technology even more competitive with traditional, high-energy intensive and costly processes such as distillation.
  • applications for large scale gas separation membrane systems are nitrogen enrichment, oxygen enrichment, hydrogen recovery, removal of hydrogen sulfide and carbon dioxide from natural gas and dehydration of air and natural gas.
  • various hydrocarbon separations are potential applications for the appropriate membrane system.
  • the membranes that are used in these applications must have high selectivity, durability, and productivity in processing large volumes of gas or liquid in order to be economically successful.
  • Membranes for gas separations have evolved rapidly in the past 25 years due to their easy processability for scale-up and low energy requirements. More than 90% of the membrane gas separation applications involve the separation of noncondensable gases: such as nitrogen from air, and hydrogen from nitrogen, argon or methane. Membrane gas separation is of special interest to petroleum producers and refiners, chemical companies, and industrial gas suppliers. Several applications of membrane gas separation have achieved commercial success, including nitrogen enrichment from air, hydrogen from nitrogen, argon or methane, carbon dioxide removal from natural gas and biogas and in enhanced oil recovery.
  • the present invention provides polyimide blend membranes.
  • This invention also pertains to the application of the polyimide blend membranes for H 2 purifications such as H 2 /CH 4 separation, and also for a variety of other gas separations such as separations of CO 2 /CH 4 , H 2 S/CH 4 , CO 2 /N 2 , olefin/paraffin separations (e.g. propylene/propane separation), and O 2 /N 2 separations.
  • H 2 purifications such as H 2 /CH 4 separation
  • other gas separations such as separations of CO 2 /CH 4 , H 2 S/CH 4 , CO 2 /N 2 , olefin/paraffin separations (e.g. propylene/propane separation), and O 2 /N 2 separations.
  • the present invention provides a polyimide blend membrane comprising a miscible blend of an aromatic polyimide I that comprises a plurality of repeating units of formula (I) and an aromatic polyimide II that comprises a plurality of repeating units of formula (II), wherein formula (I) is
  • n, m, o, and p are independent integers from 20 to 500; and wherein formula (II) is:
  • q and r are independent integers from 20 to 500; and wherein the weight ratio of said aromatic polyimide I to said aromatic polyimide II is in a range of 10:1 to 1:10.
  • the polyimide polymers used for making the polyimide blend membranes with high selectivities described in the current invention have a weight average molecular weight in the range of 50,000 to 1,000,000 Daltons, preferably between 70,000 to 500,000 Daltons.
  • the polyimide blend membrane in the present invention was prepared by blending an aromatic polyimide I with high permeability and an aromatic polyimide II with high selectivity for gas separation.
  • the polyimide blend membrane in the present invention showed improved permeability compared to the aromatic polyimide II and improved selectivity compared to the aromatic polyimide I.
  • the polyimide blend membranes in the present invention have undergone an additional UV cross-linking process.
  • the polyimide blend membranes in the present invention have UV cross-linkable benzophenone functional groups.
  • the cross-linked polyimide blend membranes comprise polymer chain segments where at least part of these polymer chain segments are cross-linked to each other through possible direct covalent bonds by exposure to UV radiation.
  • the thickness of the UV cross-linked surface layer of the polyimide blend membrane described in the present invention is in a range of 20 nm to 5 microns.
  • the cross-linking of the polyimide blend membranes provides membranes with superior selectivity and improved chemical and thermal stabilities compared to the corresponding uncross-linked polyimide blend membranes.
  • One preferred aromatic polyimide polymer I that is used for the formation of the polyimide blend membrane in the present invention is poly(3,3′,4,4′-benzophenone tetracarboxylic dianhydride-pyromellitic dianhydride-2,4,6-trimethyl-m-phenylenediamine-2,4-toluenediamine) (PI-1) derived from the condensation reaction of 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride (PMDA) with a mixture of 2,4,6-trimethyl-m-phenylenediamine (TMPDA) and 2,4-toluenediamine (2,4-TDA).
  • PI-1 poly(3,3′,4,4′-benzophenone tetracarboxylic dianhydride-pyromellitic dianhydride-2,4,6-trimethyl-m-phenylenediamine-2,4-toluenediamine)
  • the molar ratio of BTDA to PMDA is in a range of 5:1 to 1:5.
  • the molar ratio of TMPDA to 2,4-TDA is in a range of 5:1 to 1:5.
  • the molar ratio of the total dianhydrides of BTDA and PMDA to the total diamines of TMPDA and 2,4-TDA is 1:1.
  • One preferred aromatic polyimide polymer II that is used for the formation of the polyimide blend membrane in the present invention is poly(3,3′,4,4′-benzophenone tetracarboxylic dianhydride-2,4-toluenediamine-4,4′-methylenedianiline) (PI-2) derived from the condensation reaction of BTDA with a mixture of 2,4-TDA and 4,4′-methylenedianiline (MDA).
  • the molar ratio of 2,4-TDA to MDA is in a range of 10:1 to 1:10.
  • the molar ratio of BTDA dianhydride to the total diamines of 2,4-TDA and MDA is 1:1.
  • the polyimide blend membrane in the present invention can be either asymmetric integrally skinned membrane or thin film composite (TFC) membrane.
  • asymmetric integrally-skinned flat sheet or hollow fiber polyimide blend membranes in the present invention were prepared by a phase inversion process. In some cases, UV radiation was applied to the surface of the membrane to further improve the membrane selectivity.
  • the membrane dope formulation for the preparation of asymmetric integrally-skinned flat sheet or hollow fiber polyimide blend membrane with high selectivities for gas separations in the present invention comprises good solvents for the polyimide polymers that can completely dissolve the polymers.
  • Representative good solvents for use in this invention include N-methylpyrrolidone (NMP), N,N-dimethyl acetamide (DMAC), methylene chloride, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), dioxanes, 1,3-dioxolane, mixtures thereof, others known to those skilled in the art and mixtures thereof.
  • the membrane dope formulation for the preparation of asymmetric integrally-skinned flat sheet or hollow fiber polyimide blend membrane with high selectivities for gas separations in the present invention also comprises poor solvents for the polyimide polymers that cannot dissolve the polymers such as acetone, methanol, ethanol, tetrahydrofuran (THF), toluene, n-octane, n-decane, lactic acid, citric acid, isopropanol, and mixtures thereof. It is believed that the proper weight ratio of the solvents used in the present invention provides asymmetric integrally-skinned flat sheet or hollow fiber polyimide blend membrane with ⁇ 200 nm super thin nonporous selective skin layer which results in high permeances.
  • THF tetrahydrofuran
  • the thin film composite polyimide blend membrane described in the current invention comprises a thin nonporous selective separation layer comprising the polyimide blend described in the present invention and a porous nonselective mechanical support layer made from a material different from the polyimide blend described in the present invention or a polymer blend comprising a first polymer different from any of the polyimides in the polyimide blend described in the present invention and a second polymer that is the same as one of the polyimides in the polyimide blend described in the present invention.
  • the thin film composite polyimide blend membrane described in the current invention has either hollow fiber or flat sheet geometry.
  • the porous nonselective mechanical support layer has low selectivity and high flux. Selection of the porous nonselective mechanical support layer for the preparation of TFC polyimide blend membrane in the present invention may be made on the basis of the heat resistance, solvent resistance, and mechanical strength of the porous nonselective mechanical support layer, as well as other factors dictated by the operating conditions for selective permeation.
  • the porous nonselective mechanical support layer is preferably at least partially self-supporting, and in some instances may be essentially self-supporting.
  • the porous nonselective mechanical support layer may provide essentially all of the structural support for the membrane.
  • Some preferred polymers that are suitable for the preparation of the porous nonselective mechanical support layer for the TFC polyimide blend membrane according to the present invention include, but are not limited to, polysulfones, sulfonated polysulfones, polyethersulfones (PESs), sulfonated PESs, polyethers, polyetherimides such as Ultem, cellulosic polymers such as cellulose acetate and cellulose triacetate, polyamides, polyimides, polyether ketones, and blends thereof.
  • Some preferred solvents that can be used for dissolving the polyimide blends for the preparation of TFC polyimide blend membrane described in the current invention include NMP, N,N-dimethyl DMAC, methylene chloride, DMF, DMSO, dioxanes, 1,3-dioxolane, acetone, isopropanol, and mixtures thereof.
  • the polyimide blend solution has a concentration of from about 1 to about 20 wt % to provide an effective coating.
  • the dilute polyimide blend solution is applied to the surface of the porous nonselective mechanical support layer by dip-coating, spin coating, casting, spraying, painting, and other known conventional solution coating technologies.
  • the polyimide blend solution has a concentration of from about 20 to about 40 wt %.
  • the polyimide blend solution and the polymer solution for the formation of the porous nonselective mechanical support layer were co-extruded from a spinneret.
  • the invention provides a process for separating at least one gas from a mixture of gases using the polyimide blend membrane described in the present invention, the process comprising: (a) providing a polyimide blend membrane described in the present invention which is permeable to said at least one gas; (b) contacting the mixture on one side of the polyimide blend membrane described in the present invention to cause said at least one gas to permeate the membrane; and (c) removing from the opposite side of the membrane a permeate gas composition comprising a portion of said at least one gas which permeated said membrane.
  • the polyimide blend membrane described in the present invention is especially useful in the purification, separation or adsorption of a particular species in the liquid or gas phase.
  • the polyimide blend membrane described in the present invention is especially useful in gas separation processes in air purification, petrochemical, refinery, and natural gas industries.
  • separations include separation of volatile organic compounds (such as toluene, xylene, and acetone) from an atmospheric gas, such as nitrogen or oxygen and nitrogen recovery from air.
  • Further examples of such separations are for the separation of CO 2 or H 2 5 from natural gas, H 2 from N 2 , CH 4 , and Ar in ammonia purge gas streams, H 2 recovery in refineries, olefin/paraffin separations such as propylene/propane separation, and iso/normal paraffin separations.
  • any given pair or group of gases that differ in molecular size for example nitrogen and oxygen, carbon dioxide and methane, hydrogen and methane or carbon monoxide, helium and methane, can be separated using the polyimide blend membrane described in the present invention. More than two gases can be removed from a third gas.
  • some of the gas components which can be selectively removed from a raw natural gas using the membrane described herein include carbon dioxide, oxygen, nitrogen, water vapor, hydrogen sulfide, helium, and other trace gases.
  • Some of the gas components that can be selectively retained include hydrocarbon gases.
  • permeable components are acid components selected from the group consisting of carbon dioxide, hydrogen sulfide, and mixtures thereof and are removed from a hydrocarbon mixture such as natural gas
  • one module, or at least two in parallel service, or a series of modules may be utilized to remove the acid components.
  • the pressure of the feed gas may vary from 275 kPa to about 2.6 MPa (25 to 4000 psi).
  • the differential pressure across the membrane can be as low as about 70 kPa or as high as 14.5 MPa (about 10 psi or as high as about 2100 psi) depending on many factors such as the particular membrane used, the flow rate of the inlet stream and the availability of a compressor to compress the permeate stream if such compression is desired. Differential pressure greater than about 14.5 MPa (2100 psi) may rupture the membrane. A differential pressure of at least 0.7 MPa (100 psi) is preferred since lower differential pressures may require more modules, more time and compression of intermediate product streams.
  • the operating temperature of the process may vary depending upon the temperature of the feed stream and upon ambient temperature conditions.
  • the effective operating temperature of the membranes of the present invention will range from about ⁇ 50° to about 150° C. More preferably, the effective operating temperature of the polyimide blend membrane of the present invention will range from about ⁇ 20° to about 100° C., and most preferably, the effective operating temperature of the membranes of the present invention will range from about 25° to about 100° C.
  • the polyimide blend membrane described in the present invention are also especially useful in gas/vapor separation processes in chemical, petrochemical, pharmaceutical and allied industries for removing organic vapors from gas streams, e.g. in off-gas treatment for recovery of volatile organic compounds to meet clean air regulations, or within process streams in production plants so that valuable compounds (e.g., vinylchloride monomer, propylene) may be recovered.
  • gas/vapor separation processes in which the polyimide blend membrane described in the present invention may be used are hydrocarbon vapor separation from hydrogen in oil and gas refineries, for hydrocarbon dew pointing of natural gas (i.e. to decrease the hydrocarbon dew point to below the lowest possible export pipeline temperature so that liquid hydrocarbons do not separate in the pipeline), for control of methane number in fuel gas for gas engines and gas turbines, and for gasoline recovery.
  • the polyimide blend membrane described in the present invention also has immediate application to concentrate olefin in a paraffin/olefin stream for olefin cracking application.
  • the polyimide blend membrane described in the present invention can be used for propylene/propane separation to increase the concentration of the effluent in a catalytic dehydrogenation reaction for the production of propylene from propane and isobutylene from isobutane. Therefore, the number of stages of a propylene/propane splitter that is required to get polymer grade propylene can be reduced.
  • polyimide blend membrane described in the present invention is for separating isoparaffin and normal paraffin in light paraffin isomerization and MaxEneTM, a process for enhancing the concentration of normal paraffin (n-paraffin) in the naphtha cracker feedstock, which can be then converted to ethylene.
  • the polyimide blend membrane described in the present invention can also be operated at high temperature to provide the sufficient dew point margin for natural gas upgrading (e.g, CO 2 removal from natural gas).
  • the polyimide blend membrane described in the present invention can be used in either a single stage membrane or as the first or/and second stage membrane in a two stage membrane system for natural gas upgrading.
  • the mixture was mechanically stirred for 2 hours to form a homogeneous casting dope.
  • the resulting homogeneous casting dope was filtered and allowed to degas overnight.
  • the PI-1/PI-2(5:6) polyimide blend dense film membrane was prepared from the bubble free casting dope on a clean glass plate using a doctor knife with a 20-mil gap.
  • the membrane together with the glass plate was then put into a vacuum oven.
  • the solvents were removed by slowly increasing the vacuum and the temperature of the vacuum oven.
  • the membrane was dried at 200° C. under vacuum for at least 48 hours to completely remove the residual solvents to form a polymer membrane in dense film.
  • the PI-1/PI-2(5:6) polyimide blend dense film membrane was further UV cross-linked by exposure to UV radiation using 254 nm wavelength UV light with a radiation time of 10 minutes at 50° C.
  • the PI-1/PI-2(5:6) and UV cross-linked PI-1/PI-2(5:6) polyimide blend dense film membranes were tested for CO 2 /CH 4 and H 2 /CH 4 separations at 50° C. under 791 kPa (100 psig) pure gas feed pressure.
  • This membrane also has intrinsic H 2 permeability of 28.1 Barrers and single-gas H 2 /CH 4 selectivity of 139.1 at 50° C. under 791 kPa for H 2 /CH 4 separation. It can be seen from Tables 1 and 2 that the PI-1/PI-2(5:6) polyimide blend dense film membrane showed significantly improved CO 2 /CH 4 and H 2 /CH 4 selectivities after UV cross-linking
  • a hollow fiber spinning dope containing 11.9 g of PI-1 polyimide, 14.3 g of PI-2 polyimide, 65.0 g of NMP, and 6.0 g of 1,3-dioxolane was prepared.
  • the spinning dope was extruded at a flow rate of 3.0-4.0 mL/min through a spinneret at 50° C. spinning temperature.
  • a bore fluid containing 10% by weight of water in NMP was injected to the bore of the fiber at a flow rate of 0.6 mL/min simultaneously with the extruding of the spinning dope.
  • the nascent fiber traveled through an air gap length of 5-7 cm at room temperature, and then was immersed into a water coagulant bath at 19° C.
  • the water-wet fiber was annealed in a hot water bath at 85° C. for 30 minutes. The annealed water-wet fiber was then sequentially exchanged with methanol and hexane for three times and for 30 minutes each time, followed by drying at 100° C. in an oven for 1 hour to form PI-1/PI-2(5:6) polyimide blend hollow fiber membranes with the spinning conditions listed in Table 3.
  • the PI-1/PI-2(5:6) polyimide blend hollow fiber membranes prepared in Example 3 were coated with 5 wt % of thermally curable RTV silicone solution in hexane and then cured at 85° C. for 1 hour.
  • the RTV silicone-coated polyimide blend hollow fiber membranes were cross-linked via UV radiation for 2.5 minutes using a UV lamp with intensity of 1.45 mW/cm 2 .
  • the mixture was mechanically stirred for 2 hours to form a homogeneous casting dope.
  • the resulting homogeneous casting dope was filtered and allowed to degas overnight.
  • the PI-1/PI-2(6:5) polyimide blend dense film membrane was prepared from the bubble free casting dope on a clean glass plate using a doctor knife with a 20-mil gap.
  • the membrane together with the glass plate was then put into a vacuum oven.
  • the solvents were removed by slowly increasing the vacuum and the temperature of the vacuum oven.
  • the membrane was dried at 200° C. under vacuum for at least 48 hours to completely remove the residual solvents to form a polymer membrane in dense film.
  • the PI-1/PI-2(6:5) polyimide blend dense film membrane was further UV cross-linked by exposure to UV radiation using 254 nm wavelength UV light with a radiation time of 10 minutes at 50° C.
  • the PI-1/PI-2(6:5) and UV cross-linked PI-1/PI-2(6:5) polyimide blend dense film membranes were tested for CO 2 /CH 4 and H 2 /CH 4 separations at 50° C. under 791 kPa (100 psig) pure gas feed pressure.
  • This membrane also has intrinsic H 2 permeability of 36.1 Barrers and single-gas H 2 /CH 4 selectivity of 100.7 at 50° C. under 791 kPa for H 2 /CH 4 separation. It can be seen from Tables 6 and 7 that the PI-1/PI-2(6:5) polyimide blend dense film membrane showed significantly improved CO 2 /CH 4 and H 2 /CH 4 selectivities after UV cross-linking
  • a hollow fiber spinning dope containing 14.4 g of PI-1 polyimide, 12.0 g of PI-2 polyimide, 65.0 g of NMP, and 6.0 g of 1,3-dioxolane was prepared.
  • the spinning dope was extruded at a flow rate of 3.0-3.8 mL/min through a spinneret at 50° C. spinning temperature.
  • a bore fluid containing 10% by weight of water in NMP was injected to the bore of the fiber at a flow rate of 0.6 mL/min simultaneously with the extruding of the spinning dope.
  • the nascent fiber traveled through an air gap length of 7-10 cm at room temperature, and then was immersed into a water coagulant bath at 19° C.
  • the water-wet fiber was annealed in a hot water bath at 85° C. for 30 minutes. The annealed water-wet fiber was then sequentially exchanged with methanol and hexane for three times and for 30 minutes each time, followed by drying at 100° C. in an oven for 1 hour to form PI-1/PI-2(6:5) polyimide blend hollow fiber membranes with the spinning conditions listed in Table 8.
  • the PI-1/PI-2(6:5) polyimide blend hollow fiber membranes were then coated with 2 wt % of thermally curable RTV silicone solution in hexane and then cured at 100° C. for 1 hour.
  • PI-1/PI-2-6-5-O-2RTV and PI-1/PI-2-6-5-B-2RTV polyimide blend hollow fiber membranes were tested for CO 2 /CH 4 separation at 50° C. under 5617 kPa (800 psig) feed gas pressure with 10% of CO 2 and 90% of CH 4 in the feed.
  • the results are shown in Table 9. It can be seen from Table 9 that PI-1/PI-2-6-5-O-2RTV membrane described in the current invention showed CO 2 permeances of 57 GPU and high CO 2 /CH 4 selectivities of 28. PI-1/PI-2-6-5-B-2RTV membrane described in the current invention showed high CO 2 permeances of 78 GPU and high CO 2 /CH 4 selectivities of 25.5.

Abstract

The polyimide blend membrane in the present invention was prepared by blending a first aromatic polyimide with high permeability and a second aromatic polyimide with high selectivity for gas separation. The polyimide blend membrane in the present invention showed improved permeability compared to membranes made from the second aromatic polyimide and improved selectivity compared to membranes made from the first aromatic polyimide.

Description

BACKGROUND OF THE INVENTION
This invention relates to polyimide blend membranes and methods for making and using these membranes. In the past 30-35 years, the state of the art of polymer membrane-based gas separation processes has evolved rapidly. Membrane-based technologies have advantages of both low capital cost and high-energy efficiency compared to conventional separation methods. Membrane gas separation is of special interest to petroleum producers and refiners, chemical companies, and industrial gas suppliers. Several applications of membrane gas separation have achieved commercial success, including N2 enrichment from air, carbon dioxide removal from natural gas and from enhanced oil recovery, and also in hydrogen removal from nitrogen, methane, and argon in ammonia purge gas streams. For example, UOP's Separex™ cellulose acetate spiral wound polymeric membrane is currently an international market leader for carbon dioxide removal from natural gas.
Polymers provide a range of properties including low cost, permeability, mechanical stability, and ease of processability that are important for gas separation. Glassy polymers (i.e., polymers at temperatures below their Tg) have stiffer polymer backbones and therefore let smaller molecules such as hydrogen and helium pass through more quickly, while larger molecules such as hydrocarbons pass through more slowly as compared to polymers with less stiff backbones. Cellulose acetate (CA) glassy polymer membranes are used extensively in gas separation. Currently, such CA membranes are used for natural gas upgrading, including the removal of carbon dioxide. Although CA membranes have many advantages, they are limited in a number of properties including selectivity, permeability, and in chemical, thermal, and mechanical stability.
The membranes most commonly used in commercial gas and liquid separation applications are asymmetric polymeric membranes and have a thin nonporous selective skin layer that performs the separation. Separation is based on a solution-diffusion mechanism. This mechanism involves molecular-scale interactions of the permeating gas with the membrane polymer. The mechanism assumes that in a membrane having two opposing surfaces, each component is sorbed by the membrane at one surface, transported by a gas concentration gradient, and desorbed at the opposing surface. According to this solution-diffusion model, the membrane performance in separating a given pair of gases (e.g., CO2/CH4, O2/N2, H2/CH4) is determined by two parameters: the permeability coefficient (abbreviated hereinafter as permeability or PA) and the selectivity (αA/B). The PA is the product of the gas flux and the selective skin layer thickness of the membrane, divided by the pressure difference across the membrane. The αA/B is the ratio of the permeability coefficients of the two gases (αA/B=PA/PB) where PA is the permeability of the more permeable gas and PB is the permeability of the less permeable gas. Gases can have high permeability coefficients because of a high solubility coefficient, a high diffusion coefficient, or because both coefficients are high. In general, the diffusion coefficient decreases while the solubility coefficient increases with an increase in the molecular size of the gas. In high performance polymer membranes, both high permeability and selectivity are desirable because higher permeability decreases the size of the membrane area required to treat a given volume of gas, thereby decreasing capital cost of membrane units, and because higher selectivity results in a higher purity product gas.
One of the components to be separated by a membrane must have a sufficiently high permeance at the preferred conditions or an extraordinarily large membrane surface area is required to allow separation of large amounts of gases or liquids. Permeance, measured in Gas Permeation Units (GPU, 1 GPU=10−6 cm3 (STP)/cm2 s (cm Hg)), is the pressure normalized flux and is equal to permeability divided by the skin layer thickness of the membrane. Commercially available gas separation polymer membranes, such as CA, polyimide, and polysulfone membranes formed by phase inversion and solvent exchange methods have an asymmetric integrally skinned membrane structure. Such membranes are characterized by a thin, dense, selectively semipermeable surface “skin” and a less dense void-containing (or porous), non-selective support region, with pore sizes ranging from large in the support region to very small proximate to the “skin”. However, fabrication of defect-free high selectivity asymmetric integrally skinned polyimide membranes is difficult. The presence of nanopores or defects in the skin layer reduces the membrane selectivity. The high shrinkage of the polyimide membrane on cloth substrate during membrane casting and drying process results in unsuccessful fabrication of asymmetric integrally skinned polyimide flat sheet membranes using phase inversion technique.
US 2005/0268783 A1 disclosed chemically cross-linked polyimide hollow fiber membranes prepared from a monoesterified polymer followed by final cross-linking after hollow fiber formation.
U.S. Pat. No. 7,485,173 disclosed UV cross-linked mixed matrix membranes via UV radiation. The cross-linked mixed matrix membranes comprise microporous materials dispersed in the continuous UV cross-linked polymer matrix.
U.S. Pat. No. 8,016,124 disclosed a thin film composite membrane (TFC) comprising a blend of polyethersulfone and aromatic polyimide polymers. The TFC membrane has a layer of a blend of polyethersulfone and aromatic polyimide with a thickness from about 0.1 to about 3 microns.
U.S. Pat. No. 8,337,598 disclosed a TFC hollow fiber membrane with a core player and a sheath UV-crosslinked polymer layer.
The selective thin layer on the non-selective porous layer of a thin film composite (TFC) membrane can be delaminated easily from the non-selective porous layer, which will result in significantly decreased selectivity for gas separations. On the other hand, the integrally-skinned asymmetric membranes have a selective thin layer and a porous layer from the same membrane material and formed from the same membrane solution at about the same time. Therefore, the selective thin layer of an integrally-skinned asymmetric membrane cannot be delaminated easily from the non-selective porous layer.
The present invention discloses polyimide blend membranes and methods for making and using these membranes.
SUMMARY OF THE INVENTION
This invention pertains to polyimide blend membranes and methods for making and using these membranes. This invention pertains to polyimide blend thin film composite or asymmetric membrane with either flat sheet or hollow fiber geometry.
The term “polyimide blend membrane” in the present invention refers to a membrane prepared from a blend of two or more polyimide polymers.
The present invention provides a polyimide blend membrane comprising a miscible blend of an aromatic polyimide I that comprises a plurality of repeating units of formula (I) and an aromatic polyimide II that comprises a plurality of repeating units of formula (II), wherein formula (I) is
Figure US09308499-20160412-C00001
wherein n, m, o, and p are independent integers from 20 to 500; and wherein formula (II) is:
Figure US09308499-20160412-C00002
wherein q and r are independent integers from 20 to 500; and wherein the weight ratio of said aromatic polyimide I to said aromatic polyimide II is in a range of 10:1 to 1:10.
The polyimide blend membrane in the present invention was prepared by blending an aromatic polyimide I with high permeability and an aromatic polyimide II with high selectivity for gas separation. The polyimide blend membrane in the present invention showed improved permeability compared to the aromatic polyimide II and improved selectivity compared to the aromatic polyimide I.
The polyimide polymers used for making the polyimide blend membranes with high selectivities described in the current invention have a weight average molecular weight in the range of 50,000 to 1,000,000 Daltons, preferably between 70,000 to 500,000 Daltons.
In another embodiment of the invention, the polyimide blend membranes in the present invention have undergone an additional UV cross-linking process. The polyimide blend membranes in the present invention have UV cross-linkable benzophenone functional groups. The cross-linked polyimide blend membranes comprise polymer chain segments where at least part of these polymer chain segments are cross-linked to each other through possible direct covalent bonds by exposure to UV radiation. The cross-linking of the polyimide blend membranes provides membranes with superior selectivity and improved chemical and thermal stabilities compared to the corresponding uncross-linked polyimide blend membranes.
The polyimide blend membrane in the present invention can be either asymmetric integrally skinned membrane or thin film composite (TFC) membrane.
The asymmetric integrally-skinned flat sheet or hollow fiber polyimide blend membranes in the present invention were prepared by a phase inversion process. In some cases, UV radiation was applied to the surface of the membrane to further improve the membrane selectivity.
The membrane dope formulation for the preparation of asymmetric integrally-skinned flat sheet or hollow fiber polyimide blend membrane with high selectivities for gas separations in the present invention comprises good solvents for the polyimide polymers that can completely dissolve the polymers. Representative good solvents for use in this invention include N-methylpyrrolidone (NMP), N,N-dimethyl acetamide (DMAC), methylene chloride, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), dioxanes, 1,3-dioxolane, mixtures thereof, others known to those skilled in the art and mixtures thereof. In some cases, the membrane dope formulation for the preparation of asymmetric integrally-skinned flat sheet or hollow fiber polyimide blend membrane with high selectivities for gas separations in the present invention also comprises poor solvents for the polyimide polymers that cannot dissolve the polymers such as acetone, methanol, ethanol, tetrahydrofuran (THF), toluene, n-octane, n-decane, lactic acid, citric acid, isopropanol, and mixtures thereof. It is believed that the proper weight ratio of the solvents used in the present invention provides asymmetric integrally-skinned flat sheet or hollow fiber polyimide blend membrane with <200 nm super thin nonporous selective skin layer which results in high permeances.
The thin film composite polyimide blend membrane described in the current invention comprises a thin nonporous selective separation layer comprising the polyimide blend described in the present invention and a porous nonselective mechanical support layer made from a material different from the polyimide blend described in the present invention or a polymer blend comprising a first polymer different from any of the polyimides in the polyimide blend described in the present invention and a second polymer that is the same as one of the polyimides in the polyimide blend described in the present invention. The porous nonselective mechanical support layer described in the present invention with a low selectivity and high flux can be made from materials including cellulosic polymers, polysulfone, polyethersulfone, polyamide, polyimide, polyetherimide, cellulose nitrate, polyurethane, polycarbonate, polystyrene, polybenzoxazole, or mixtures thereof.
One asymmetric integrally-skinned hollow fiber polyimide blend membrane PI-1/PI-2 described in the present invention is fabricated from a blend of a poly(3,3′,4,4′-benzophenone tetracarboxylic dianhydride-pyromellitic dianhydride-2,4,6-trimethyl-m-phenylenediamine-2,4-toluenediamine) (PI-1) derived from the condensation reaction of 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride (PMDA) with a mixture of 2,4,6-trimethyl-m-phenylenediamine (TMPDA) and 2,4-toluenediamine (2,4-TDA) (BTDA:PMDA:TMPDA:2,4-TDA=3:2:3:2 (molar ratio) and a poly(3,3′,4,4′-benzophenone tetracarboxylic dianhydride-2,4-toluenediamine-4,4′-methylenedianiline) (PI-2) derived from the condensation reaction of BTDA with a mixture of 2,4-TDA and 4,4′-methylenedianiline (MDA) (BTDA:2,4-TDA:MDA=5:4:1 (molar ratio). The weight ratio of PI-1 to PI-2 is 1:1.2. The blend PI-1/PI-2-O-5Si2.5U asymmetric integrally-skinned hollow fiber membrane with 2.5 minutes of UV treatment showed high H2/CH4 separation performance with H2 permeance of 198 GPU and H2/CH4 selectivity of 184 for H2/CH4 separation. The blend PI-1/PI-2-O-5Si2.5U asymmetric integrally-skinned hollow fiber membrane with 2.5 minutes of UV treatment also showed high CO2/CH4 separation performance with CO2 permeance of 74 GPU and CO2/CH4 selectivity of 30.1 for CO2/CH4 separation.
The invention provides a process for separating at least one gas from a mixture of gases using the polyimide blend membrane described herein, the process comprising: (a) providing a polyimide blend membrane described in the present invention which is permeable to said at least one gas; (b) contacting the mixture on one side of the polyimide blend membrane to cause said at least one gas to permeate the membrane; and (c) removing from the opposite side of the membrane a permeate gas composition comprising a portion of said at least one gas which permeated said membrane.
The polyimide blend membranes described in the current invention are not only suitable for H2 purification application, but also suitable for a variety of other gas separations such as CO2/CH4, O2/N2, and H2S/CH4 separations.
DETAILED DESCRIPTION OF THE INVENTION
The use of membranes for separation of both gases and liquids is a growing technological area with potentially high economic reward due to the low energy requirements and the potential for scaling up of modular membrane designs. Advances in membrane technology, with the continuing development of new membrane materials and new methods for the production of high performance membranes will make this technology even more competitive with traditional, high-energy intensive and costly processes such as distillation. Among the applications for large scale gas separation membrane systems are nitrogen enrichment, oxygen enrichment, hydrogen recovery, removal of hydrogen sulfide and carbon dioxide from natural gas and dehydration of air and natural gas. Also, various hydrocarbon separations are potential applications for the appropriate membrane system. The membranes that are used in these applications must have high selectivity, durability, and productivity in processing large volumes of gas or liquid in order to be economically successful. Membranes for gas separations have evolved rapidly in the past 25 years due to their easy processability for scale-up and low energy requirements. More than 90% of the membrane gas separation applications involve the separation of noncondensable gases: such as nitrogen from air, and hydrogen from nitrogen, argon or methane. Membrane gas separation is of special interest to petroleum producers and refiners, chemical companies, and industrial gas suppliers. Several applications of membrane gas separation have achieved commercial success, including nitrogen enrichment from air, hydrogen from nitrogen, argon or methane, carbon dioxide removal from natural gas and biogas and in enhanced oil recovery.
The present invention provides polyimide blend membranes. This invention also pertains to the application of the polyimide blend membranes for H2 purifications such as H2/CH4 separation, and also for a variety of other gas separations such as separations of CO2/CH4, H2S/CH4, CO2/N2, olefin/paraffin separations (e.g. propylene/propane separation), and O2/N2 separations.
The present invention provides a polyimide blend membrane comprising a miscible blend of an aromatic polyimide I that comprises a plurality of repeating units of formula (I) and an aromatic polyimide II that comprises a plurality of repeating units of formula (II), wherein formula (I) is
Figure US09308499-20160412-C00003
wherein n, m, o, and p are independent integers from 20 to 500; and wherein formula (II) is:
Figure US09308499-20160412-C00004
wherein q and r are independent integers from 20 to 500; and wherein the weight ratio of said aromatic polyimide I to said aromatic polyimide II is in a range of 10:1 to 1:10.
The polyimide polymers used for making the polyimide blend membranes with high selectivities described in the current invention have a weight average molecular weight in the range of 50,000 to 1,000,000 Daltons, preferably between 70,000 to 500,000 Daltons.
The polyimide blend membrane in the present invention was prepared by blending an aromatic polyimide I with high permeability and an aromatic polyimide II with high selectivity for gas separation. The polyimide blend membrane in the present invention showed improved permeability compared to the aromatic polyimide II and improved selectivity compared to the aromatic polyimide I.
In another embodiment of the invention, the polyimide blend membranes in the present invention have undergone an additional UV cross-linking process. The polyimide blend membranes in the present invention have UV cross-linkable benzophenone functional groups. The cross-linked polyimide blend membranes comprise polymer chain segments where at least part of these polymer chain segments are cross-linked to each other through possible direct covalent bonds by exposure to UV radiation. The thickness of the UV cross-linked surface layer of the polyimide blend membrane described in the present invention is in a range of 20 nm to 5 microns. The cross-linking of the polyimide blend membranes provides membranes with superior selectivity and improved chemical and thermal stabilities compared to the corresponding uncross-linked polyimide blend membranes.
One preferred aromatic polyimide polymer I that is used for the formation of the polyimide blend membrane in the present invention is poly(3,3′,4,4′-benzophenone tetracarboxylic dianhydride-pyromellitic dianhydride-2,4,6-trimethyl-m-phenylenediamine-2,4-toluenediamine) (PI-1) derived from the condensation reaction of 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride (PMDA) with a mixture of 2,4,6-trimethyl-m-phenylenediamine (TMPDA) and 2,4-toluenediamine (2,4-TDA). The molar ratio of BTDA to PMDA is in a range of 5:1 to 1:5. The molar ratio of TMPDA to 2,4-TDA is in a range of 5:1 to 1:5. The molar ratio of the total dianhydrides of BTDA and PMDA to the total diamines of TMPDA and 2,4-TDA is 1:1.
One preferred aromatic polyimide polymer II that is used for the formation of the polyimide blend membrane in the present invention is poly(3,3′,4,4′-benzophenone tetracarboxylic dianhydride-2,4-toluenediamine-4,4′-methylenedianiline) (PI-2) derived from the condensation reaction of BTDA with a mixture of 2,4-TDA and 4,4′-methylenedianiline (MDA). The molar ratio of 2,4-TDA to MDA is in a range of 10:1 to 1:10. The molar ratio of BTDA dianhydride to the total diamines of 2,4-TDA and MDA is 1:1.
The polyimide blend membrane in the present invention can be either asymmetric integrally skinned membrane or thin film composite (TFC) membrane.
The asymmetric integrally-skinned flat sheet or hollow fiber polyimide blend membranes in the present invention were prepared by a phase inversion process. In some cases, UV radiation was applied to the surface of the membrane to further improve the membrane selectivity.
The membrane dope formulation for the preparation of asymmetric integrally-skinned flat sheet or hollow fiber polyimide blend membrane with high selectivities for gas separations in the present invention comprises good solvents for the polyimide polymers that can completely dissolve the polymers. Representative good solvents for use in this invention include N-methylpyrrolidone (NMP), N,N-dimethyl acetamide (DMAC), methylene chloride, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), dioxanes, 1,3-dioxolane, mixtures thereof, others known to those skilled in the art and mixtures thereof. In some cases, the membrane dope formulation for the preparation of asymmetric integrally-skinned flat sheet or hollow fiber polyimide blend membrane with high selectivities for gas separations in the present invention also comprises poor solvents for the polyimide polymers that cannot dissolve the polymers such as acetone, methanol, ethanol, tetrahydrofuran (THF), toluene, n-octane, n-decane, lactic acid, citric acid, isopropanol, and mixtures thereof. It is believed that the proper weight ratio of the solvents used in the present invention provides asymmetric integrally-skinned flat sheet or hollow fiber polyimide blend membrane with <200 nm super thin nonporous selective skin layer which results in high permeances.
The thin film composite polyimide blend membrane described in the current invention comprises a thin nonporous selective separation layer comprising the polyimide blend described in the present invention and a porous nonselective mechanical support layer made from a material different from the polyimide blend described in the present invention or a polymer blend comprising a first polymer different from any of the polyimides in the polyimide blend described in the present invention and a second polymer that is the same as one of the polyimides in the polyimide blend described in the present invention. The thin film composite polyimide blend membrane described in the current invention has either hollow fiber or flat sheet geometry.
The porous nonselective mechanical support layer has low selectivity and high flux. Selection of the porous nonselective mechanical support layer for the preparation of TFC polyimide blend membrane in the present invention may be made on the basis of the heat resistance, solvent resistance, and mechanical strength of the porous nonselective mechanical support layer, as well as other factors dictated by the operating conditions for selective permeation. The porous nonselective mechanical support layer is preferably at least partially self-supporting, and in some instances may be essentially self-supporting. The porous nonselective mechanical support layer may provide essentially all of the structural support for the membrane. Some preferred polymers that are suitable for the preparation of the porous nonselective mechanical support layer for the TFC polyimide blend membrane according to the present invention include, but are not limited to, polysulfones, sulfonated polysulfones, polyethersulfones (PESs), sulfonated PESs, polyethers, polyetherimides such as Ultem, cellulosic polymers such as cellulose acetate and cellulose triacetate, polyamides, polyimides, polyether ketones, and blends thereof.
Some preferred solvents that can be used for dissolving the polyimide blends for the preparation of TFC polyimide blend membrane described in the current invention include NMP, N,N-dimethyl DMAC, methylene chloride, DMF, DMSO, dioxanes, 1,3-dioxolane, acetone, isopropanol, and mixtures thereof. For the preparation of TFC polyimide blend flat sheet membrane, it is preferred that the polyimide blend solution has a concentration of from about 1 to about 20 wt % to provide an effective coating. The dilute polyimide blend solution is applied to the surface of the porous nonselective mechanical support layer by dip-coating, spin coating, casting, spraying, painting, and other known conventional solution coating technologies. For the preparation of TFC polyimide blend hollow fiber membrane, it is preferred that the polyimide blend solution has a concentration of from about 20 to about 40 wt %. The polyimide blend solution and the polymer solution for the formation of the porous nonselective mechanical support layer were co-extruded from a spinneret.
The invention provides a process for separating at least one gas from a mixture of gases using the polyimide blend membrane described in the present invention, the process comprising: (a) providing a polyimide blend membrane described in the present invention which is permeable to said at least one gas; (b) contacting the mixture on one side of the polyimide blend membrane described in the present invention to cause said at least one gas to permeate the membrane; and (c) removing from the opposite side of the membrane a permeate gas composition comprising a portion of said at least one gas which permeated said membrane.
The polyimide blend membrane described in the present invention is especially useful in the purification, separation or adsorption of a particular species in the liquid or gas phase.
The polyimide blend membrane described in the present invention is especially useful in gas separation processes in air purification, petrochemical, refinery, and natural gas industries. Examples of such separations include separation of volatile organic compounds (such as toluene, xylene, and acetone) from an atmospheric gas, such as nitrogen or oxygen and nitrogen recovery from air. Further examples of such separations are for the separation of CO2 or H25 from natural gas, H2 from N2, CH4, and Ar in ammonia purge gas streams, H2 recovery in refineries, olefin/paraffin separations such as propylene/propane separation, and iso/normal paraffin separations. Any given pair or group of gases that differ in molecular size, for example nitrogen and oxygen, carbon dioxide and methane, hydrogen and methane or carbon monoxide, helium and methane, can be separated using the polyimide blend membrane described in the present invention. More than two gases can be removed from a third gas. For example, some of the gas components which can be selectively removed from a raw natural gas using the membrane described herein include carbon dioxide, oxygen, nitrogen, water vapor, hydrogen sulfide, helium, and other trace gases. Some of the gas components that can be selectively retained include hydrocarbon gases. When permeable components are acid components selected from the group consisting of carbon dioxide, hydrogen sulfide, and mixtures thereof and are removed from a hydrocarbon mixture such as natural gas, one module, or at least two in parallel service, or a series of modules may be utilized to remove the acid components. For example, when one module is utilized, the pressure of the feed gas may vary from 275 kPa to about 2.6 MPa (25 to 4000 psi). The differential pressure across the membrane can be as low as about 70 kPa or as high as 14.5 MPa (about 10 psi or as high as about 2100 psi) depending on many factors such as the particular membrane used, the flow rate of the inlet stream and the availability of a compressor to compress the permeate stream if such compression is desired. Differential pressure greater than about 14.5 MPa (2100 psi) may rupture the membrane. A differential pressure of at least 0.7 MPa (100 psi) is preferred since lower differential pressures may require more modules, more time and compression of intermediate product streams. The operating temperature of the process may vary depending upon the temperature of the feed stream and upon ambient temperature conditions. Preferably, the effective operating temperature of the membranes of the present invention will range from about −50° to about 150° C. More preferably, the effective operating temperature of the polyimide blend membrane of the present invention will range from about −20° to about 100° C., and most preferably, the effective operating temperature of the membranes of the present invention will range from about 25° to about 100° C.
The polyimide blend membrane described in the present invention are also especially useful in gas/vapor separation processes in chemical, petrochemical, pharmaceutical and allied industries for removing organic vapors from gas streams, e.g. in off-gas treatment for recovery of volatile organic compounds to meet clean air regulations, or within process streams in production plants so that valuable compounds (e.g., vinylchloride monomer, propylene) may be recovered. Further examples of gas/vapor separation processes in which the polyimide blend membrane described in the present invention may be used are hydrocarbon vapor separation from hydrogen in oil and gas refineries, for hydrocarbon dew pointing of natural gas (i.e. to decrease the hydrocarbon dew point to below the lowest possible export pipeline temperature so that liquid hydrocarbons do not separate in the pipeline), for control of methane number in fuel gas for gas engines and gas turbines, and for gasoline recovery.
The polyimide blend membrane described in the present invention also has immediate application to concentrate olefin in a paraffin/olefin stream for olefin cracking application. For example, the polyimide blend membrane described in the present invention can be used for propylene/propane separation to increase the concentration of the effluent in a catalytic dehydrogenation reaction for the production of propylene from propane and isobutylene from isobutane. Therefore, the number of stages of a propylene/propane splitter that is required to get polymer grade propylene can be reduced. Another application for the polyimide blend membrane described in the present invention is for separating isoparaffin and normal paraffin in light paraffin isomerization and MaxEne™, a process for enhancing the concentration of normal paraffin (n-paraffin) in the naphtha cracker feedstock, which can be then converted to ethylene.
The polyimide blend membrane described in the present invention can also be operated at high temperature to provide the sufficient dew point margin for natural gas upgrading (e.g, CO2 removal from natural gas). The polyimide blend membrane described in the present invention can be used in either a single stage membrane or as the first or/and second stage membrane in a two stage membrane system for natural gas upgrading.
EXAMPLES
The following examples are provided to illustrate one or more preferred embodiments of the invention, but are not limited embodiments thereof. Numerous variations can be made to the following examples that lie within the scope of the invention.
Example 1 Preparation of PI-1/PI-2(5:6) and UV Cross-Linked PI-1/PI-2(5:6) Polyimide Blend Dense Film Membranes
2.5 g of aromatic polyimide poly(3,3′,4,4′-benzophenone tetracarboxylic dianhydride-pyromellitic dianhydride-2,4,6-trimethyl-m-phenylenediamine-2,4-toluenediamine) (PI-1) containing UV cross-linkable carbonyl groups and 3.0 g of poly(3,3′,4,4′-benzophenone tetracarboxylic dianhydride-2,4-toluenediamine-4,4′-methylenedianiline) (PI-2) containing UV cross-linkable carbonyl groups were dissolved in a solvent mixture of 12.0 g of NMP and 15.0 g of 1,3-dioxolane. The mixture was mechanically stirred for 2 hours to form a homogeneous casting dope. The resulting homogeneous casting dope was filtered and allowed to degas overnight. The PI-1/PI-2(5:6) polyimide blend dense film membrane was prepared from the bubble free casting dope on a clean glass plate using a doctor knife with a 20-mil gap. The membrane together with the glass plate was then put into a vacuum oven. The solvents were removed by slowly increasing the vacuum and the temperature of the vacuum oven. Finally, the membrane was dried at 200° C. under vacuum for at least 48 hours to completely remove the residual solvents to form a polymer membrane in dense film.
The PI-1/PI-2(5:6) polyimide blend dense film membrane was further UV cross-linked by exposure to UV radiation using 254 nm wavelength UV light with a radiation time of 10 minutes at 50° C.
Example 2 Evaluation of the CO2/CH4 and H2/CH4 Separation Performance of PI-1/PI-2(5:6) and UV Cross-Linked PI-1/PI-2(5:6) Polyimide Blend Dense Film Membranes Prepared in Example 1
The PI-1/PI-2(5:6) and UV cross-linked PI-1/PI-2(5:6) polyimide blend dense film membranes were tested for CO2/CH4 and H2/CH4 separations at 50° C. under 791 kPa (100 psig) pure gas feed pressure. The results in Tables 1 and 2 show that the new PI-1/PI-2(5:6) polyimide blend dense film membrane has intrinsic CO2 permeability of 6.94 Barrers (1 Barrer=10−10 cm3 (STP) cm/cm2 s (cm Hg)) and single-gas CO2/CH4 selectivity of 34.4 at 50° C. under 791 kPa for CO2/CH4 separation. This membrane also has intrinsic H2 permeability of 28.1 Barrers and single-gas H2/CH4 selectivity of 139.1 at 50° C. under 791 kPa for H2/CH4 separation. It can be seen from Tables 1 and 2 that the PI-1/PI-2(5:6) polyimide blend dense film membrane showed significantly improved CO2/CH4 and H2/CH4 selectivities after UV cross-linking
TABLE 1
Pure gas permeation test results of PI-1/PI-2(5:6) and UV
cross-linked PI-1/PI-2(5:6) polyimide blend
dense film membranes for CO2/CH4 separation *
Dense Film Membrane PCO2 (Barrer) αCO2/CH4
PI-1/PI-2(5:6) 6.94 34.4
UV cross-linked PI-1/PI-2(5:6) 6.33 48.0
* PCO2 and PCH4 were tested at 50° C. and 791 kPa (100 psig);
1 Barrer = 10−10 cm3(STP).cm/cm2.sec.cmHg.
TABLE 2
Pure gas permeation test results of PI-1/PI-2(5:6) and UV
cross-linked PI-1/PI-2(5:6) polyimide blend dense film
membranes for H2/CH4 separation *
Dense Film Membrane PH2 (Barrer) αCO2/CH4
PI-1/PI-2(5:6) 28.1 139.1
UV cross-linked PI-1/PI-2(5:6) 27.6 209.0
* PH2 and PCH4 were tested at 50° C. and 791 kPa (100 psig);
1 Barrer = 10−10 cm3(STP).cm/cm2.sec.cmHg.
Example 3 Preparation of PI-1/PI-2(5:6) Polyimide Blend Hollow Fiber Membranes
A hollow fiber spinning dope containing 11.9 g of PI-1 polyimide, 14.3 g of PI-2 polyimide, 65.0 g of NMP, and 6.0 g of 1,3-dioxolane was prepared. The spinning dope was extruded at a flow rate of 3.0-4.0 mL/min through a spinneret at 50° C. spinning temperature. A bore fluid containing 10% by weight of water in NMP was injected to the bore of the fiber at a flow rate of 0.6 mL/min simultaneously with the extruding of the spinning dope. The nascent fiber traveled through an air gap length of 5-7 cm at room temperature, and then was immersed into a water coagulant bath at 19° C. and wound up at a rate of 23-30 m/min. The water-wet fiber was annealed in a hot water bath at 85° C. for 30 minutes. The annealed water-wet fiber was then sequentially exchanged with methanol and hexane for three times and for 30 minutes each time, followed by drying at 100° C. in an oven for 1 hour to form PI-1/PI-2(5:6) polyimide blend hollow fiber membranes with the spinning conditions listed in Table 3.
TABLE 3
Spinning conditions for PI-1/PI-2(5:6) polyimide blend
hollow fiber membranes
Hollow Fiber Air gap Dope rate Bore rate Take-up rate
Membrane (cm) (mL/min) (mL/min) (m/min)
PI-1/PI-2-O 5 3.0 0.6 23.5
PI-1/PI-2-P 5 3.0 0.6 30.2
PI-1/PI-2-W 10  3.6 0.6 23.5
PI-1/PI-2-Y 7 3.0 0.6 23.5
PI-1/PI-2-G 3 4.0 0.6 30.2
Example 4 Preparation of UV cross-linked PI-1/PI-2(5:6) polyimide blend hollow fiber membranes
The PI-1/PI-2(5:6) polyimide blend hollow fiber membranes prepared in Example 3 were coated with 5 wt % of thermally curable RTV silicone solution in hexane and then cured at 85° C. for 1 hour. The RTV silicone-coated polyimide blend hollow fiber membranes were cross-linked via UV radiation for 2.5 minutes using a UV lamp with intensity of 1.45 mW/cm2.
Example 5 Evaluation of CO2/CH4 Separation Performance of UV Cross-Linked PI-1/PI-2(5:6) Polyimide Blend Hollow Fiber Membranes
The PI-1/PI-2-O-5Si2.5U, PI-1/PI-2-P-5Si2.5U, and PI-1/PI-2-Y-5Si2.5U UV cross-linked polyimide blend hollow fiber membranes were tested for CO2/CH4 separation at 50° C. under 5617 kPa (800 psig) feed gas pressure with 10% of CO2 and 90% of CH4 in the feed. The results are shown in Table 4. It can be seen from Table 4 that all membranes described in the current invention showed high CO2 permeances of 68-74 GPU and high CO2/CH4 selectivities of 28-30.
TABLE 4
CO2/CH4 separation performance of PI-1/PI-2(5:6) and UV
cross-linked PI-1/PI-2(5:6) polyimide blend hollow fiber membranes
Membrane CO2 permeance (GPU) CO2/CH4 selectivity
PI-1/PI-2-O-5Si2.5U 73.7 30.1
PI-1/PI-2-P-5Si2.5U 70.2 30.3
PI-1/PI-2-Y-5Si2.5U 68.1 28.2
1 GPU = 10−6 cm3 (STP)/cm2 s (cm Hg)Testing conditions: 50° C., 5617 kPa (800 psig) feed gas pressure, 10% CO2 and 90% of CH4 in the feed.
Example 6 Evaluation of H2/CH4 Separation Performance of UV Cross-Linked PI-1/PI-2(5:6) Polyimide Blend Hollow Fiber Membranes
The PI-1/PI-2-O-5Si2.5U, PI-1/PI-2-P-5Si2.5U, and PI-1/PI-2-Y-5Si2.5U UV cross-linked polyimide blend hollow fiber membranes were tested for H2/CH4 separation at 50° C. under 5617 kPa (800 psig) feed gas pressure with 10% of H2 and 90% of CH4 in the feed. The results are shown in Table 5. It can be seen from Table 5 that all membranes described in the current invention showed high H2 permeances of 187-232 GPU and high H2/CH4 selectivities of 145-224.
TABLE 5
H2/CH4 separation performance of PI-1/PI-2(5:6) and UV cross-
linked PI-1/PI-2(5:6) polyimide blend hollow fiber membranes
H2 permeance H2/CH4
Membrane (GPU) selectivity
PI-1/PI-2-O-5Si2.5U 198.1 184.2
PI-1/PI-2-P-5Si2.5U 231.6 224.0
PI-1/PI-2-Y-5Si2.5U 187.3 145.1
1 GPU = 10−6 cm3 (STP)/cm2 s (cm Hg)Testing conditions: 50° C., 5617 kPa (800 psig) feed gas pressure, 10% H2 and 90% of CH4 in the feed.
Example 7 Preparation of PI-1/PI-2(6:5) and UV Cross-Linked PI-1/PI-2(6:5) Polyimide Blend Dense Film Membranes
3.0 G of aromatic polyimide poly(3,3′,4,4′-benzophenone tetracarboxylic dianhydride-pyromellitic dianhydride-2,4,6-trimethyl-m-phenylenediamine-2,4-toluenediamine) (PI-1) containing UV cross-linkable carbonyl groups and 2.5 g of poly(3,3′,4,4′-benzophenone tetracarboxylic dianhydride-2,4-toluenediamine-4,4′-methylenedianiline) (PI-2) containing UV cross-linkable carbonyl groups were dissolved in a solvent mixture of 12.0 g of NMP and 15.0 g of 1,3-dioxolane. The mixture was mechanically stirred for 2 hours to form a homogeneous casting dope. The resulting homogeneous casting dope was filtered and allowed to degas overnight. The PI-1/PI-2(6:5) polyimide blend dense film membrane was prepared from the bubble free casting dope on a clean glass plate using a doctor knife with a 20-mil gap. The membrane together with the glass plate was then put into a vacuum oven. The solvents were removed by slowly increasing the vacuum and the temperature of the vacuum oven. Finally, the membrane was dried at 200° C. under vacuum for at least 48 hours to completely remove the residual solvents to form a polymer membrane in dense film.
The PI-1/PI-2(6:5) polyimide blend dense film membrane was further UV cross-linked by exposure to UV radiation using 254 nm wavelength UV light with a radiation time of 10 minutes at 50° C.
Example 8 Evaluation of the CO2/CH4 and H2/CH4 Separation Performance of PI-1/PI-2(6:5) and UV Cross-Linked PI-1/PI-2(6:5) Polyimide Blend Dense Film Membranes Prepared in Example 7
The PI-1/PI-2(6:5) and UV cross-linked PI-1/PI-2(6:5) polyimide blend dense film membranes were tested for CO2/CH4 and H2/CH4 separations at 50° C. under 791 kPa (100 psig) pure gas feed pressure. The results in Tables 6 and 7 show that the new PI-1/PI-2(6:5) polyimide blend dense film membrane has intrinsic CO2 permeability of 10.8 Barrers (1 Barrer=1010 cm3 (STP) cm/cm2 s (cm Hg)) and single-gas CO2/CH4 selectivity of 30.0 at 50° C. under 791 kPa for CO2/CH4 separation. This membrane also has intrinsic H2 permeability of 36.1 Barrers and single-gas H2/CH4 selectivity of 100.7 at 50° C. under 791 kPa for H2/CH4 separation. It can be seen from Tables 6 and 7 that the PI-1/PI-2(6:5) polyimide blend dense film membrane showed significantly improved CO2/CH4 and H2/CH4 selectivities after UV cross-linking
TABLE 6
Pure gas permeation test results of PI-1/PI-2(6:5) and UV
cross-linked PI-1/PI-2(6:5) polyimide blend dense film
membranes for CO2/CH4 separation *
Dense Film Membrane PCO2 (Barrer) αCO2/CH4
PI-1/PI-2(6:5) 10.8 30.0
UV cross-linked PI-1/PI-2(6:5) 9.40 36.3
* PCO2 and PCH4 were tested at 50° C. and 791 kPa (100 psig);
1 Barrer = 10−10 cm3(STP).cm/cm2.sec.cmHg.
TABLE 7
Pure gas permeation test results of PI-1/PI-2(6:5) and UV
cross-linked PI-1/PI-2(6:5) polyimide blend dense film
membranes for H2/CH4 separation *
Dense Film Membrane PH2 (Barrer) αCO2/CH4
PI-1/PI-2(6:5) 36.1 100.7
UV cross-linked PI-1/PI-2(6:5) 35.2 135.9
* PH2 and PCH4 were tested at 50° C. and 791 kPa (100 psig);
1 Barrer = 10−10 cm3(STP).cm/cm2.sec.cmHg.
Example 9 Preparation of PI-1/PI-2(6:5) Polyimide Blend Hollow Fiber Membranes
A hollow fiber spinning dope containing 14.4 g of PI-1 polyimide, 12.0 g of PI-2 polyimide, 65.0 g of NMP, and 6.0 g of 1,3-dioxolane was prepared. The spinning dope was extruded at a flow rate of 3.0-3.8 mL/min through a spinneret at 50° C. spinning temperature. A bore fluid containing 10% by weight of water in NMP was injected to the bore of the fiber at a flow rate of 0.6 mL/min simultaneously with the extruding of the spinning dope. The nascent fiber traveled through an air gap length of 7-10 cm at room temperature, and then was immersed into a water coagulant bath at 19° C. and wound up at a rate of 23-30 m/min. The water-wet fiber was annealed in a hot water bath at 85° C. for 30 minutes. The annealed water-wet fiber was then sequentially exchanged with methanol and hexane for three times and for 30 minutes each time, followed by drying at 100° C. in an oven for 1 hour to form PI-1/PI-2(6:5) polyimide blend hollow fiber membranes with the spinning conditions listed in Table 8. The PI-1/PI-2(6:5) polyimide blend hollow fiber membranes were then coated with 2 wt % of thermally curable RTV silicone solution in hexane and then cured at 100° C. for 1 hour.
TABLE 8
Spinning conditions for PI-1/PI-2(6:5) polyimide blend hollow
fiber membranes
Air gap Dope rate Bore rate Take-up rate
Hollow Fiber Membrane (cm) (mL/min) (mL/min) (m/min)
PI-1/PI-2-6-5-O-2RTV 7 3.8 0.6 30.2
PI-1/PI-2-6-5-G-2RTV 7 3.8 0.6 23.5
PI-1/PI-2-6-5-B-2RTV 7 3.0 0.6 23.5
Example 10 Evaluation of CO2/CH4 Separation Performance of PI-1/PI-2(6:5) Polyimide Blend Hollow Fiber Membranes
The PI-1/PI-2-6-5-O-2RTV and PI-1/PI-2-6-5-B-2RTV polyimide blend hollow fiber membranes were tested for CO2/CH4 separation at 50° C. under 5617 kPa (800 psig) feed gas pressure with 10% of CO2 and 90% of CH4 in the feed. The results are shown in Table 9. It can be seen from Table 9 that PI-1/PI-2-6-5-O-2RTV membrane described in the current invention showed CO2 permeances of 57 GPU and high CO2/CH4 selectivities of 28. PI-1/PI-2-6-5-B-2RTV membrane described in the current invention showed high CO2 permeances of 78 GPU and high CO2/CH4 selectivities of 25.5.
TABLE 9
CO2/CH4 separation performance of PI-1/PI-2(6:5)
polyimide blend hollow fiber membranes
Membrane CO2 permeance (GPU) CO2/CH4 selectivity
PI-1/PI-2-6-5-O-2RTV 57.0 28.0
PI-1/PI-2-6-5-B-2RTV 77.8 25.5
1 GPU = 10−6 cm3 (STP)/cm2 s (cm Hg)Testing conditions: 50° C., 5617 kPa (800 psig) feed gas pressure, 10% CO2 and 90% of CH4 in the feed.
Example 11 Evaluation of H2/CH4 Separation Performance of PI-1/PI-2(6:5) Polyimide Blend Hollow Fiber Membranes
The PI-1/PI-2-6-5-G-2RTV and PI-1/PI-2-6-5-B-2RTV polyimide blend hollow fiber membranes were tested for H2/CH4 separation at 50° C. under 5617 kPa (800 psig) feed gas pressure with 10% of H2 and 90% of CH4 in the feed. The results are shown in Table 10. It can be seen from Table 10 that both membranes described in the current invention showed high H2 permeances of 285-298 GPU and high H2/CH4 selectivities of about 150-160.
TABLE 10
H2/CH4 separation performance of PI-1/PI-2(6:5)
polyimide blend hollow fiber membranes
Membrane H2 permeance (GPU) H2/CH4 selectivity
PI-1/PI-2-6-5-G-2RTV 285 149.7
PI-1/PI-2-6-5-B-2RTV 298 161.9
1 GPU = 10−6 cm3 (STP)/cm2 s (cm Hg)Testing conditions: 50° C., 5617 kPa (800 psig) feed gas pressure, 10% H2 and 90% of CH4 in the feed.

Claims (10)

The invention claimed is:
1. A polyimide blend membrane comprising a miscible blend of a first aromatic polyimide that comprises a plurality of repeating units of formula (I) and a second aromatic polyimide that comprises a plurality of repeating units of formula (II), wherein formula (I) is represented by:
Figure US09308499-20160412-C00005
wherein n, m, o, and p are independent integers from 20 to 500; and wherein formula (II) is represented by:
Figure US09308499-20160412-C00006
wherein q and r are independent integers from 20 to 500; and wherein the weight ratio of said first aromatic polyimide to said second aromatic polyimide is in a range from about 10:1 to 1:10.
2. The polyimide blend membrane of claim 1 wherein said membrane is an asymmetric integrally skinned membrane or a thin film composite membrane.
3. The polyimide blend membrane of claim 1 wherein said first aromatic polyimide has high permeability relative to said second polyimide and said second aromatic polyimide has high selectivity relative to said first aromatic polyimide.
4. The polyimide blend membrane of claim 1 wherein said polyimide blend membrane is cross-linked via UV radiation.
5. The polyimide blend membrane of claim 2 wherein said thin film composite membrane further comprises a porous nonselective mechanical support layer made from a material different from polyimide blend material.
6. The polyimide blend membrane of claim 2 wherein said thin film composite membrane further comprises a porous nonselective mechanical support layer made from a polymer blend comprising a first polymer different from the polyimides in the said polyimide blend and a second polymer the same as one of the polyimides in the said polyimide blend.
7. The polyimide blend membrane of claim 1 wherein said first aromatic polymer and said second aromatic polymer have a weight average molecular weight in a range from 50,000 to 1,000,000 Daltons.
8. The polyimide blend membrane of claim 1 comprising polymer chain segments wherein said polymer chain segments are cross-linked to a polymer chain segment through direct covalent bonds.
9. The polyimide blend membrane of claim 5 wherein said porous nonselective mechanical support layer comprises a material selected from the group consisting of cellulosic polymers, polysulfone, polyethersulfone, polyamide, polyimide, polyetherimide, cellulose nitrate, polyurethane, polycarbonate, polystyrene, polybenzoxazole, or mixtures thereof.
10. The polyimide blend membrane of claim 4 wherein a UV cross-linked surface layer of said polyimide blend membrane has a thickness in a range from about 20 nm to 5 microns.
US14/496,789 2014-09-25 2014-09-25 Polyimide blend membranes for gas separations Active US9308499B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
US14/496,789 US9308499B1 (en) 2014-09-25 2014-09-25 Polyimide blend membranes for gas separations

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US14/496,789 US9308499B1 (en) 2014-09-25 2014-09-25 Polyimide blend membranes for gas separations

Publications (2)

Publication Number Publication Date
US20160089634A1 US20160089634A1 (en) 2016-03-31
US9308499B1 true US9308499B1 (en) 2016-04-12

Family

ID=55583450

Family Applications (1)

Application Number Title Priority Date Filing Date
US14/496,789 Active US9308499B1 (en) 2014-09-25 2014-09-25 Polyimide blend membranes for gas separations

Country Status (1)

Country Link
US (1) US9308499B1 (en)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB201510648D0 (en) * 2015-06-17 2015-07-29 Fujifilm Mfg Europe Bv Composite membranes
US10328386B2 (en) * 2017-05-18 2019-06-25 Uop Llc Co-cast thin film composite flat sheet membranes for gas separations and olefin/paraffin separations

Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4113628A (en) * 1974-06-05 1978-09-12 E. I. Du Pont De Nemours And Company Asymmetric polyimide membranes
US5085676A (en) * 1990-12-04 1992-02-04 E. I. Du Pont De Nemours And Company Novel multicomponent fluid separation membranes
US20040107830A1 (en) * 2002-12-02 2004-06-10 Simmons John W Polyimide blends for gas separation membranes
US7247191B2 (en) 2001-12-20 2007-07-24 Chevron U.S.A. Inc. Crosslinked and crosslinkable hollow fiber membrane and method of making same utility
US7485173B1 (en) 2005-12-15 2009-02-03 Uop Llc Cross-linkable and cross-linked mixed matrix membranes and methods of making the same
US20100317751A1 (en) * 2006-10-19 2010-12-16 Paulus Theodorus Maria Van Brugge Process for the extraction of hydrogen from a gas mixture
US8016124B2 (en) 2009-04-22 2011-09-13 Honeywell International Inc. Thin film gas separation membranes
US20120322911A1 (en) * 2011-06-17 2012-12-20 Uop Llc. Polyimide gas separation membranes
US8337598B2 (en) 2008-09-05 2012-12-25 Honeywell International Inc. Photo-crosslinked gas selective membranes as part of thin film composite hollow fiber membranes

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4113628A (en) * 1974-06-05 1978-09-12 E. I. Du Pont De Nemours And Company Asymmetric polyimide membranes
US5085676A (en) * 1990-12-04 1992-02-04 E. I. Du Pont De Nemours And Company Novel multicomponent fluid separation membranes
US7247191B2 (en) 2001-12-20 2007-07-24 Chevron U.S.A. Inc. Crosslinked and crosslinkable hollow fiber membrane and method of making same utility
US20040107830A1 (en) * 2002-12-02 2004-06-10 Simmons John W Polyimide blends for gas separation membranes
US7485173B1 (en) 2005-12-15 2009-02-03 Uop Llc Cross-linkable and cross-linked mixed matrix membranes and methods of making the same
US20100317751A1 (en) * 2006-10-19 2010-12-16 Paulus Theodorus Maria Van Brugge Process for the extraction of hydrogen from a gas mixture
US8337598B2 (en) 2008-09-05 2012-12-25 Honeywell International Inc. Photo-crosslinked gas selective membranes as part of thin film composite hollow fiber membranes
US8016124B2 (en) 2009-04-22 2011-09-13 Honeywell International Inc. Thin film gas separation membranes
US20120322911A1 (en) * 2011-06-17 2012-12-20 Uop Llc. Polyimide gas separation membranes

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
U.S. Appl. No. 14/496,754, filed Sep. 25, 2014.

Also Published As

Publication number Publication date
US20160089634A1 (en) 2016-03-31

Similar Documents

Publication Publication Date Title
US8366804B2 (en) High permeance polyimide membranes for air separation
US8614288B2 (en) Polyimide gas separation membranes
US8704030B2 (en) Process of separating gases using polyimide membranes
US8912288B2 (en) Separation process using a polyimide membrane
US9567436B2 (en) Super high selectivity aromatic block copolyimide membranes for separations
US9669363B2 (en) High permeance membranes for gas separations
US8710173B2 (en) Blend polymer gas separation membrane
US9233344B1 (en) High selectivity polyimide membrane for natural gas upgrading and hydrogen purification
WO2015047702A1 (en) Self cross-linkable and self cross-linked aromatic polyimide membranes for separations
US20140290478A1 (en) High performance cross-linked polyimide asymmetric flat sheet membranes
WO2014209699A1 (en) High permeability copolyimide gas separation membranes
US9266058B1 (en) High selectivity polyimide membrane for natural gas upgrading and hydrogen purification
US9480954B2 (en) High selectivity epoxysilicone-cross-linked polyimide membranes for gas separations
US9751053B2 (en) Asymmetric integrally-skinned flat sheet membranes for H2 purification and natural gas upgrading
US9308487B1 (en) Polyimide blend membranes for gas separations
US9308499B1 (en) Polyimide blend membranes for gas separations
EP3197853A1 (en) Asymmetric integrally-skinned flat sheet membranes for h2 purification and natural gas upgrading
US9662616B2 (en) Aromatic alkyl-substituted polyethersulfone and UV-cross-linked aromatic alkyl-substituted polyethersulfone membranes for gas sepratations
US11786861B2 (en) High selectivity polyimide/PES blend hollow fiber membrane for gas separations
US9000122B1 (en) Aromatic poly (ether sulfone imide) membranes for gas separations

Legal Events

Date Code Title Description
AS Assignment

Owner name: UOP LLC, ILLINOIS

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:LIU, CHUNQING;TRAN, HOWIE Q;REEL/FRAME:034980/0837

Effective date: 20141216

STCF Information on status: patent grant

Free format text: PATENTED CASE

MAFP Maintenance fee payment

Free format text: PAYMENT OF MAINTENANCE FEE, 4TH YEAR, LARGE ENTITY (ORIGINAL EVENT CODE: M1551); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY

Year of fee payment: 4

MAFP Maintenance fee payment

Free format text: PAYMENT OF MAINTENANCE FEE, 8TH YEAR, LARGE ENTITY (ORIGINAL EVENT CODE: M1552); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY

Year of fee payment: 8